1. Field of the Invention
The present invention relates to a fluid injection control system and, more particularly, to such a system that is used to control the injection of fluid into a plurality of wellbores.
2. Description of the Prior Art
After a hydrocarbon-bearing subterranean formation has ceased producing fluid under its own pressure, a form of artificial lift is utilized to bring the hydrocarbons to the surface. After artificial lift has been utilized, then it is oftentimes advisable to use some form of fluid injection to drive the hydrocarbons from the injection well(s) to one or more production wells. The drive fluid can include water, inert gases (such as nitrogen and carbon dioxide), and waterflooding chemicals, usually surfactants. The injection of fluid increases the quantity of hydrocarbon production and prolongs the economic life of the field.
In the injection of fluid into a hydrocarbon bearing subterranean formation, there is a need for accurate control of the quantity of fluid injected, as well as the pressure at which the fluid is injected. If too little fluid is injected, then the optimum drive mechanism may not be established and all of the available hydrocarbons cannot be recovered. Also, if the injection pressure exceeds the parting or fracture pressure (commonly referred to as the bottomhole treating pressure) of the formation, cracks can form within the formation to provide channeling from the injection well to the production well so that the fluid passes directly through channels and not out into the formation to sweep or drive the hydrocarbons to the production wells.
Various fluid injection control systems utilizing computers have been described and used in the past to accurately control the injection of fluids into an injection well. Two such systems are described in U.S. Pat. No. 4,374,544 and U.S. patent application Ser. No. 546,614 filed Oct. 28, 1983 now U.S. Pat. No. 4,615,390 .The latter system is also described in the article "Solar Powered Controller Improves Water Injection," World Oil, April 1981. Both of these prior art systems, as well as all fluid injection control systems known to the inventors hereof, are located at each injection wellhead. In these systems, each injection well includes a pressure transducer, a flow measuring device, such as a turbine meter, and a Remote Terminal Unit (RTU) which is in communication via a hardwire or radio link to a controlling computer, commonly referred to as a host computer. As beneficial as the prior art systems are in the control of the injection of fluid, the arrangements described in the prior art systems are not preferable for use with a radial injection system.
A radial injection system, as is well known to those skilled in the art, includes a large volume feed of fluid that passes into a fluid distribution device, called a header, which includes a plurality of controlled outlets. Each outlet is in communication via a conduit to an injection well. The benefits of such a radial injection system is that at a central location the control of the injection of the fluid into each well can be accomplished without the need for the injection control personnel to travel to each wellhead, which may be spaced several miles apart each from the other. By using a radial injection system, the manpower cost, as well as equipment maintenance, is greatly reduced.
The problem with using the prior art systems on a radial injection system is that each wellhead would include an RTU, a turbine meter, a pressure transducer, necessary control valves, and several miles of hardwire cable and/or expensive communication equipment so that each wellhead can communicate to a control facility. There exists a need for a simple, inexpensive, and accurate control system for the injection of fluid into a plurality of wellbores from a single location to eliminate the need for placing the control equipment at each well- head.